A low-magnetic high-efficiency neutron and gamma composite shielding material for a fusion reactor and a preparation method thereof

Abstract

This invention discloses a low-magnetic, high-efficiency neutron and gamma composite shielding material for fusion reactors and its preparation method. The composite material, by mass percentage, comprises the following components: 80.0–95.0% tungsten boride powder, 5.0–10.0% Gd₂O₃ powder, and 0.5–4.0% ceramic and non-metallic activating aid. The metallic activating aid includes an activating component and a stabilizing component. The activating component is B₄C, and the stabilizing component is MgO or Y₂O₃. By introducing a ceramic and non-metallic activation system composed of B₄C and MgO or Y₂O₃, this invention not only achieves the densification and homogenization of tungsten boride and Gd₂O₃ materials without introducing magnetism and ensuring low magnetic permeability, but also enables pressureless sintering by combining spray granulation and cold isostatic pressing processes.

Description

Technical Field

[0001] This invention relates to the field of fusion reactor and reactor internal component material design and technology, and more specifically, to a low-magnetic, high-efficiency neutron and gamma composite shielding material for fusion reactors and its preparation method. Background Technology

[0002] Magnetic confinement fusion reactors integrate auxiliary systems such as superconducting magnets, vacuum chambers, diagnostic control systems, and high-power power supplies. Among these, the superconducting magnet, with its complex structure, is the core system for maintaining plasma confinement and achieving steady-state operation of the reactor core. However, the operating environment of fusion reactors is extremely harsh, with neutron energies reaching 14 MeV. Without adequate shielding, neutrons and gamma rays can damage the magnet, severely affecting its function and jeopardizing the safe operation of the fusion reactor. Therefore, providing effective shielding for the superconducting magnet and related systems within the reactor is crucial for ensuring the stability, reliability, and safety of the fusion reactor. Due to the limited internal space, miniaturization and weight reduction are critical in the design of fusion reactors. The operating conditions and environment, such as strong magnetic fields, high and low temperatures (windows and magnet side), and small volume (limited space), must be fully considered. Material systems must be designed to fully utilize material properties to improve shielding efficiency and performance, significantly saving design space for internal components of the fusion reactor.

[0003] The shielding performance of neutrons and gamma rays is primarily determined by the elemental properties of the material. Gamma ray shielding requires elements with high atomic numbers, while neutron shielding performance is mainly determined by the neutron absorption cross-section of the elements in the material. The higher the neutron absorption cross-section and the higher the content of the elements, the better the neutron shielding performance. Among the many neutron-absorbing elements, Gd has the largest thermal neutron absorption cross-section. Low atomic number elements like boron (B) have a strong ability to absorb neutrons and can moderate them, exhibiting a large neutron absorption cross-section over a wide energy range. W has a large scattering cross-section for high-energy neutrons and, due to its high density, provides strong shielding against gamma rays. Furthermore, fusion reactors operate in strong magnetic field environments, requiring materials to be non-magnetic or low-magnetic to avoid affecting the magnetic field environment of the fusion reactor.

[0004] Effective design of these elements to address the radiation protection requirements, comprehensive shielding performance, and quality control in the confined spaces and special locations of fusion reactors will greatly satisfy the high-efficiency neutron and gamma composite shielding requirements of fusion reactor shielding materials and components, enabling customized protection for different locations and energy spectra.

[0005] Tungsten boride materials have good application potential in comprehensive shielding systems due to their high density, boron content, and good high-temperature stability. Gd2O3 has good mechanical properties and the largest thermal neutron absorption cross section. Adding it as a reinforcement to tungsten boride can further improve the material's ability to absorb thermal neutrons. However, tungsten boride is a difficult-to-sinter system with strong covalent bonds and a low interparticle self-diffusion rate. Gd2O3 is a high-melting-point oxide, and its introduction will further increase the number of heterogeneous interfaces, leading to problems such as difficulty in particle rearrangement, residual interfacial pores, and local stress concentration, resulting in a decrease in material density.

[0006] The applicant's research found that introducing metallic sintering aids such as Ni, Fe, and Co can improve the interfacial bonding between tungsten boride particles and rare earth oxide particles, thereby significantly improving the density and mechanical properties of ceramic sintering. While these metallic elements contribute to increased density, they can also introduce paramagnetic or ferromagnetic responses into the material, and even cause increased permeability fluctuations in localized segregation regions, making the material difficult to meet the application requirements in low-magnetic environments.

[0007] Therefore, how to improve the sintering density of ceramics while minimizing the introduction of magnetic metal sintering aids, and achieve the preparation of materials with low magnetic permeability and high uniformity, is an urgent problem to be solved.

[0008] Meanwhile, the hot pressing process is generally required in the preparation of composite materials to improve local density to some extent. However, hot pressing equipment usually places high demands on mold size, heating zone size, high-temperature pressure head load-bearing capacity, and temperature field uniformity, making it difficult to simultaneously handle large-sized parts, complex-shaped parts, and continuous production of multiple specifications. Taking a circular plate-shaped component with a diameter of 20 cm as an example, under a sintering pressure of 40 MPa, the hot pressing equipment needs to continuously apply an axial load of approximately 1256.6 kN at high temperature, which places high demands on equipment tonnage and system stability, and results in low output per furnace and significant costs associated with scaling up.

[0009] In view of the above, this application is hereby submitted. Summary of the Invention

[0010] Tungsten boride, as a composite shielding material for gamma and neutrons, generally exhibits poor thermal neutron shielding performance. Although the introduction of rare earth oxides can comprehensively improve shielding performance, the tungsten boride-rare earth oxide system suffers from difficulties in densification, numerous interfacial pores, insufficient mechanical strength, and low stability in engineering manufacturing. To address these technical issues, this invention provides a low-magnetic, high-efficiency neutron and gamma composite shielding material for fusion reactors and its preparation method. By introducing a ceramic and non-metallic activation system composed of B4C and MgO or Y2O3, not only can the densification and homogenization of tungsten boride and Gd2O3 materials be achieved without introducing magnetism, ensuring the material's low magnetic permeability, but it can also be combined with processes such as spray granulation and cold isostatic pressing to achieve pressureless sintering.

[0011] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a low-magnetic, high-efficiency neutron and gamma composite shielding material for fusion reactors, comprising the following components by mass percentage: 80.0-95.0% tungsten boride powder, 5.0-10.0% Gd₂O₃ powder, and 0.5-4.0% ceramic and non-metallic activating sintering aid; The ceramic and non-metallic activating sintering aid includes an activating component and a stabilizing component. The activating component is B4C, and the stabilizing component is MgO or Y2O3.

[0012] This invention adds Gd₂O₃ to a tungsten boride matrix, which comprehensively improves the composite shielding performance of tungsten boride materials against thermal neutrons, fast neutrons, high-energy neutrons, and gamma rays. Simultaneously, this invention introduces a ceramic and non-metallic activation system composed of B₄C and MgO or Y₂O₃. B₄C acts as a surface activating component, while MgO or Y₂O₃ acts as a grain boundary pinning and microstructure stabilizing component. Without introducing magnetic materials, these fine non-metallic particles fill the voids between large ceramic particles, increasing the contact points between particles, shortening the atomic diffusion distance, accelerating the sintering process, and improving the interfacial bonding between tungsten boride particles and Gd₂O₃ particles. This significantly improves the sintering activation degree of the tungsten boride-Gd₂O₃ system, ensuring that the introduction of Gd₂O₃ improves the material's shielding performance while achieving sufficient densification. This significantly improves the material's density, shielding performance, and overall mechanical properties, while maintaining low magnetic properties.

[0013] In one specific embodiment, the content of B4C is 0.2-3.0%, and the content of MgO or Y2O3 is 0.1-2.0%.

[0014] In one specific embodiment, the tungsten boride powder includes at least one of WB, WB2, and W2B5. This can improve the sintering density in terms of particle size distribution and sintering packing efficiency. In one specific embodiment, the particle size of the Gd2O3 powder is 50–500 nm.

[0015] In one specific embodiment, the tungsten boride powder includes at least one of W2B, WB, WB2, W2B5, and WB4. In actual preparation, a mixture of two or three of WB, WB2, and W2B5 can also be used.

[0016] In one specific embodiment, the median particle size of the tungsten boride powder and Gd2O3 powder is 1-3 mm, which can ensure the uniformity of mixing, contact area and driving force for subsequent sintering.

[0017] Secondly, the present invention provides a method for preparing a low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors, comprising the following steps: S1. Weigh out the multiphase tungsten boride powder, nano-sized Gd2O3 powder, and B4C, MgO, or Y2O3 powder according to the design ratio, and record the batch number, purity, particle size range, and moisture content of the raw materials.

[0018] S2. Add a dispersing medium, dispersant and temporary binder to the powder to form a uniform slurry; homogenize the powder by wet ball milling, three-dimensional mixing or a combination of both, with the ball milling time preferably being 4 to 16 hours.

[0019] S3. Spray granulation of the uniform slurry to obtain spherical or near-spherical particles with good flowability, thereby improving the uniformity of mold filling and the consistency of batch molding. The preferred particle size of the granulated particles is 30–120 mm.

[0020] S4. The granulated powder is first subjected to low-pressure molding or pre-pressing to form a preform, and then subjected to cold isostatic pressing. The preferred pre-pressing pressure is 5 to 50 MPa, and the cold isostatic pressing pressure is 120 to 320 MPa, in order to reduce the density gradient inside the large-sized component.

[0021] S5. Heat the green body to 300-700℃ at a rate of 0.5-3℃ / min for degreasing and removing adhesive, and keep it at that temperature for 0.5-3 hours.

[0022] S6. Perform stepwise heating sintering under vacuum, argon or other protective atmosphere, heating to 1200-1500℃ at 2-5℃ / min and holding for 0.5-2 h to promote surface purification and early diffusion activation; then heat to 1700-1900℃ and hold for 1-4 h to complete uniform densification under pressureless conditions.

[0023] S7 performs cutting, grinding, dimensional trimming, and performance testing on sintered bodies. The testing items include magnetic permeability, relative density, dimensional deviation, mechanical properties, and shielding performance.

[0024] This invention utilizes a ceramic and non-metallic activation system composed of B4C and MgO or Y2O3, combined with spray granulation and cold isostatic pressing (CIP) processes. First, the sintering aids undergo a dissolution-precipitation mechanism at high temperatures, resulting in a denser composite material after sintering. Second, spray granulation ensures that the non-metallic aids are uniformly coated within the ceramic matrix, making it easier to form porous and smooth spherical particles after granulation. This creates continuous and uniform channels, facilitating uniform wetting of all particles and resulting in a more uniform and dense material. Finally, the CIP process applies isotropic pressure, eliminating pressure gradients and making the raw material density more uniform. This ensures uniform shrinkage during heating, preventing the formation of air bubbles and internal defects. These three factors work synergistically to promote pressureless densification sintering, achieving high density and improved mechanical properties of the material.

[0025] This invention introduces a ceramic and non-metallic activation sintering aid system composed of B4C and MgO or Y2O3 to replace the metal sintering agent. It can achieve dense co-sintering of tungsten boride and Gd2O3 through pressureless sintering without the need for hot pressing. This eliminates the limitations of hot pressing sintering, which is restricted by the shape of the mold and is only suitable for preparing ceramic parts with simple shapes that are difficult to sinter. Furthermore, hot pressing sintering is also limited by the high cost of equipment and large-size graphite molds.

[0026] The method of this invention adds ceramic and non-metallic sintering aids and utilizes a pressureless sintering process to significantly improve the density uniformity of large-size green bodies and reduce the performance differences between the center and edge regions. It is suitable for the continuous preparation of large-size plates, rings, and modular components. At the same time, the ceramic and non-metallic sintering aid system can inhibit abnormal grain growth, which helps to reduce the risk of sintering cracking, warping, and dimensional instability, and improve the consistency of batch products.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The present invention provides a low-magnetic, high-efficiency neutron and gamma composite shielding material and its preparation method for fusion reactors. Through the design and optimization of the material element composition, it can meet the requirements of narrow space, complex construction, and high-efficiency shielding in the preparation of internal components of fusion reactors. 2. The present invention provides a low-magnetic, high-efficiency neutron and gamma composite shielding material for fusion reactors and its preparation method. It adopts a ceramic and non-metallic activation system composed of B4C and MgO or Y2O3, which can achieve densification and microstructure control of tungsten boride and Gd2O3 composite materials without introducing magnetic metal sintering aids. The magnetic permeability of the material can be controlled at m≤1.05, reducing the impact on the magnetic field environment of the fusion reactor. 3. The present invention provides a low-magnetic, high-efficiency neutron and gamma composite shielding material and preparation method for fusion reactors. By performing segmented sintering, the "interface activation" stage and the "high-temperature densification" stage can be carried out separately, which is beneficial to balance early particle rearrangement and later structure stability, and reduce the risk of abnormal grain growth caused by simply holding the temperature for a long time. 4. The present invention provides a low-magnetic, high-efficiency neutron and gamma composite shielding material for fusion reactors and its preparation method. It introduces a ceramic and non-metallic activated sintering aid system composed of B4C and MgO or Y2O3 to replace the metal sintering agent. The dense co-sintering of tungsten boride and Gd2O3 can be achieved through pressureless sintering without the need for hot pressing. This eliminates the limitations of hot pressing sintering, which is restricted by the shape of the mold and is only suitable for preparing ceramic parts with simple shapes that are difficult to sinter. Furthermore, hot pressing sintering is also limited by the high cost of equipment and large-size graphite molds.

[0028] 5. The low-magnetic, high-efficiency neutron and gamma composite shielding material and its preparation method for fusion reactors provided in this embodiment of the invention can significantly improve the density uniformity of large-size blanks, reduce the performance differences between the center and edge regions, and is suitable for the continuous preparation of large-size plates, rings and modular components. At the same time, the ceramic and non-metallic sintering aid system can inhibit abnormal grain growth, which helps to reduce the risk of sintering cracking, warping and dimensional instability, and improve the consistency of batch products. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 The XRD pattern of the composite shielding material provided in Embodiment 1 of the present invention; Figure 2 The room temperature magnetization curve of the composite shielding material provided in Embodiment 1 of the present invention; Figure 3 Metallographic and SEM images of the composite shielding material surface provided in Embodiment 1 of the present invention; Figure 4 The XRD pattern of the composite shielding material provided in Embodiment 2 of the present invention; Figure 5 Metallographic and SEM images of the composite shielding material surface provided in Embodiment 2 of the present invention; Figure 6 The room temperature magnetization curve of the composite shielding material provided in Embodiment 2 of the present invention; Figure 7The XRD pattern of the composite shielding material provided in Comparative Example 1 of this invention; Figure 8 SEM image of the composite shielding material provided in Comparative Example 1 of this invention; Figure 9 Metallographic and SEM images of the composite shielding material surface provided in Comparative Example 2 of this invention; Figure 10 Metallographic and SEM images of the composite shielding material surface provided in Comparative Example 3 of this invention; Figure 11 The room temperature magnetization curve of the composite shielding material surface provided in Comparative Example 3 of this invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0032] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known materials or methods have not been specifically described in order to avoid obscuring the invention.

[0033] Throughout this specification, references to “an embodiment,” “an example,” or “an example” mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases “an embodiment,” “an example,” “an example,” or “an example” appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0034] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0036] Example 1 This invention provides a method for preparing a low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors, comprising the following steps: S1. Weigh out 91.0 wt.% WB powder, 7.0 wt.% nano-sized Gd2O3 powder, 1.2 wt.% B4C powder, and 0.8 wt.% Y2O3 powder according to the designed ratio, and record the batch number, purity, particle size range, and moisture content of the raw materials.

[0037] S2. Add the above powder to an ethanol system containing a dispersant and a small amount of polyvinyl alcohol binder, and perform wet ball milling for 8 hours to obtain a uniform slurry.

[0038] S3. Spray granulation of the uniform slurry, the particle size of the granulated particles is mainly distributed in the range of 40 to 90 μm.

[0039] S4. The granulated powder is first pre-molded by molding, and then cold isostatically pressed at 240 MPa for 10 min to prepare a plate-shaped blank with dimensions of 250 mm × 250 mm × 10 mm.

[0040] S5. The green body is heated to 550℃ at 2℃ / min and held for 1 h for degreasing, then heated to 1400℃ at 4℃ / min and held for 1 h, and finally heated to 1840℃ and held for 2 h for pressureless sintering.

[0041] The density of the composite shielding material sample was tested using the water displacement method, and the final sample density reached 97.6%.

[0042] The specific process of the drainage method is as follows: (1) Place the sample in a 105℃ oven and dry for 1-2 hours until the mass no longer changes. Then take it out and put it in a desiccator for later use. (2) Weigh the dried sample on a precision balance, i.e., the mass M1 of the sample in air; (3) Place the sample into a wide-mouth bottle and fill the bottle with deionized water. Use a vacuum pump to evacuate the bottle until the pores in the sample are filled with deionized water. (4) Gently place the sample into the self-made tray under the electronic balance, immerse it in deionized water, and weigh the sample mass M2; (5) Remove the sample from the immersion liquid, wipe off the excess liquid on the surface, and ensure that the liquid inside the sample cannot be extracted. Immediately weigh the saturated mass M3 in the air. According to Archimedes' principle, the formula for calculating the porosity of a sample is as follows: P = (M3 - M1) / (M3 - M2) × 100% M1 ------- The mass (g) of the sample in air after drying; M2 ------- The mass (g) of the sample in water after it has fully absorbed water; M3-------The mass (g) of the sample in air after it has fully absorbed water.

[0043] XRD patterns of the obtained composite shielding material are as follows: Figure 1 As shown, it mainly exists as a single WB phase, with a relative density difference of less than 0.3% between the center and the edge. The composite shielding material has a room temperature magnetic permeability of 1.003, and its magnetization curve is shown in the figure. Figure 2 As shown, the sample surface is flat, with no obvious warping or cracking.

[0044] Metallographic and SEM images of the composite shielding material sample surface, such as... Figure 3 As shown in the figure, the sample surface has good density.

[0045] The room temperature compressive strength of the composite shielding material sample (tested according to standard GB / T 4740-2024) is 1246 MPa; the gamma ray strength of the composite shielding material sample is... 60 The linear attenuation coefficient of Co is 0.718 cm. -1 ; 0.0253 eV thermal neutron macroscopic cross section 178.5 cm -1 The half-value layer thickness is 0.0039 cm; the macroscopic cross-section of the 14 MeV fast neutron is 0.29 cm. -1 The half-value layer thickness is 2.383 cm, indicating that it exhibits good synergistic attenuation capability for both types of radiation.

[0046] gamma rays 60 Co linear attenuation coefficient measurement method: Place the sample in 60 After the Co gamma source, the attenuation ratio with and without the sample is measured, the protection efficiency is calculated, and then the linear attenuation coefficient is calculated by fitting the formula.

[0047] Example 2 This invention provides a method for preparing a low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors, comprising the following steps: S1. Weigh out 89.5 wt.% WB powder, 8.5 wt.% nano-sized Gd2O3 powder, 1.0 wt.% B4C powder, and 1.0 wt.% MgO powder according to the designed proportions, and record the batch number, purity, particle size range, and moisture content of the raw materials.

[0048] S2. Add the above powder to an ethanol system containing a dispersant and a small amount of polyvinyl alcohol binder, and perform wet ball milling for 8 hours to obtain a uniform slurry.

[0049] S3. Spray granulation of the uniform slurry, the particle size of the granulated particles is mainly distributed in the range of 40 to 90 μm.

[0050] S4. The granulated powder is first pre-molded by molding, and then cold isostatically pressed at 260 MPa for 10 min to prepare a plate-shaped blank with a size of 200 mm, an inner diameter of 100 mm, and a thickness of 20 mm.

[0051] S5. The green body is heated to 600℃ at 1.5℃ / min and held for 1.5 h, then heated to 1450℃ at 3.5℃ / min and held for 40 min, and then heated to 1860℃ and held for 2 h for pressureless sintering.

[0052] The density of the composite shielding material sample was tested using the water displacement method, and the final sample density reached 97.3%.

[0053] XRD patterns of the obtained composite shielding material are as follows: Figure 4As shown, it mainly exists as a single WB phase, with small amounts of W2B and WC present on the surface. Metallographic and SEM images of the composite shielding material sample surface are shown below. Figure 5 As shown, the annular sample exhibits good surface compactness, with a relative density difference of less than 0.4% between the center and the edge. The composite shielding material has a room temperature magnetic permeability of 1.0024, and its magnetization curve is shown below. Figure 6 As shown, the tissue is relatively uniform and the overall dimensional stability is good.

[0054] The room temperature compressive strength of the composite shielding material sample is 1204 MPa; the gamma ray strength of the composite shielding material sample is... 60 The linear attenuation coefficient of Co is 0.704 cm⁻¹. -1 The macroscopic cross section of a 0.0253 eV thermal neutron is 204.3 cm. -1 The half-value layer thickness is 0.0034 cm; the macroscopic cross-section of the 14 MeV fast neutron is 0.28 cm. -1 The half-value layer thickness is 2.442 cm, indicating that it exhibits good synergistic attenuation capability for both types of radiation.

[0055] Comparative Example 1 This comparative example provides a method for preparing a tungsten boride shielding material, including the following steps: Weigh 100% of WB powder and add it to anhydrous ethanol. Perform planetary ball milling for 8 hours using zirconia balls as the grinding medium. After milling, dry at 80℃ for 10 hours. The median particle size of the resulting mixed powder is approximately 3 mm.

[0056] WB powder was placed into a graphite mold, spread and compacted, and then placed in a hot pressing sintering furnace for vacuum hot pressing sintering. First, it was pre-pressed at room temperature, then heated to 500℃ at a rate of 10℃ / min and held for 1 hour to remove organic residues; then heated to 1400℃ at a rate of 5℃ / min and held for 60 minutes, with the pressure of the press head gradually increased to 5MPa. Finally, the temperature was further increased to 1750℃ and held for 2 hours before furnace cooling.

[0057] The density of the sintered sample was tested using the water displacement method, and the density was divided by the theoretical density to obtain a density of 95%; the XRD results are as follows. Figure 7 As shown, it exists as a single phase in Western blotting (WB) with no other impurities; the SEM results are as follows: Figure 8 As shown: The results show that the bulk material is basically dense, with micropores in some areas, and the room temperature magnetic permeability of the material is 1.0002.

[0058] The material has a room temperature compressive strength of 1100 MPa; 100% WB bulk gamma ray... 60 The linear attenuation coefficient of Co is 0.82 cm. -1The macroscopic cross section of a 0.0253 eV thermal neutron is 41.45 cm. -1 The half-value layer thickness is 0.0167 cm; the macroscopic cross-section of the 14MeV fast neutron is 0.32 cm. -1 The half-value layer thickness is 2.184 cm.

[0059] Compared with Examples 1 and 2, this comparative example did not add rare earth oxide Gd₂O₃ or ceramic and non-metallic sintering aids. It can be seen that the gamma-ray and 14MeV fast neutron shielding performance, compressive strength, and magnetic permeability of this comparative example are comparable to those of Examples 1 and 2. This indicates that for these examples, the addition of Gd₂O₃ and ceramic and non-metallic sintering aids not only did not degrade the original shielding and mechanical properties of tungsten boride, but also significantly improved the corresponding mechanical and shielding properties through a reasonable ratio of Gd₂O₃ and the aids. Furthermore, the magnetic permeability data also shows that the addition of Gd₂O₃ and the aids did not introduce magnetic materials. This ensures the low magnetic properties of the material and its application in fusion reactor shielding materials. Furthermore, the thermal neutron shielding performance of this comparative example is significantly lower than that of Example 1, especially the macroscopic cross-section of the thermal neutron is much smaller. This is because this comparative example did not add Gd2O3, while the addition of Gd2O3 in the examples significantly improved the material's thermal neutron shielding performance, meeting the high-efficiency neutron and gamma composite shielding requirements of fusion reactor shielding materials. Finally, the density of Example 1 is also higher than that of this comparative example, indicating that by adding ceramic and non-metallic sintering aids, the interfacial bonding problem caused by the introduction of Gd2O3 in the examples was solved, achieving dense co-firing of tungsten boride and Gd2O3.

[0060] Comparative Example 2 This comparative example provides a method for preparing a low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors, comprising the following steps: The mixture consisted of 91.0 wt.% tungsten boride powder, 7.0 wt.% nano-sized Gd₂O₃ powder, and 2.0 wt.% metallic Ni powder. The powders were added to an ethanol system containing a dispersant and a small amount of polyvinyl alcohol binder, and then wet-milled for 10 h to obtain a uniform slurry. The slurry was then spray-granulated, and the particle size after granulation was mainly distributed between 40 and 90 μm.

[0061] The granulated powder was first pre-formed by molding, and then cold isostatically pressed at 240 MPa for 10 min to prepare a circular green body with a diameter ≥120 mm × 10 mm. The green body was degreased by heating to 600℃ at 2℃ / min and holding for 1 h, then heated to 1400℃ at 4℃ / min and holding for 1 h, and finally heated to 1900℃ and held for 2 h for pressureless sintering.

[0062] The obtained circular sample had a relative density of 92.7%, with a relative density difference of less than 0.8% between the center and the edge. The room temperature magnetic permeability was 1.03. The sample surface was smooth, with no obvious warping or cracking. Figure 9 The surface metallographic and SEM images of the material show that there are many pores on the surface, and the degree of densification is not high.

[0063] The room temperature compressive strength is 734 MPa; gamma ray strength. 60 The linear attenuation coefficient of Co is 0.75 cm. -1 The macroscopic cross section of a 0.0253 eV thermal neutron is 182.62 cm⁻¹. -1 The half-value layer thickness is 0.0038 cm; the macroscopic cross-section of the 14 MeV fast neutron is 0.30 cm. -1 The half-value layer thickness is 2.321 cm.

[0064] Compared to Example 1, this comparative example uses a metal sintering aid instead of the ceramic and non-metallic sintering aids of the present invention, while employing the same pressureless sintering process. It can be seen that the neutron and gamma shielding performance of the material in this comparative example is comparable to that of Example 1, because both the comparative example and the example use Gd₂O₃. However, the room temperature permeability of this comparative example is significantly increased. This is because the addition of the metal sintering aid introduces magnetic elements, leading to an increase in material permeability, which limits its application in fusion reactor shielding materials. Furthermore, the compressive strength and density of the material in this comparative example are significantly reduced. This is because although the addition of the metal sintering aid in this comparative example can improve the interfacial wetting and rearrangement capabilities between tungsten boride and Gd₂O₃, under pressureless sintering, the metal sintering aid is insufficient to address the problems of weak interfacial bonding and pore concentration. In contrast, the ceramic and non-metallic sintering aids used in the example can fill the voids between large ceramic particles with fine non-metallic particles, increasing the contact points between particles and shortening the atomic diffusion distance. Therefore, pressureless sintering can achieve material densification.

[0065] Comparative Example 3 This comparative example provides a method for preparing a low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors, comprising the following steps: Weigh the following components by mass percentage: 91.0 wt.% WB powder, 7.0 wt.% Gd₂O₃ powder, 1.2 wt.% B₄C powder, and 0.8 wt.% Y₂O₃ powder. Add the above powders to anhydrous ethanol and ball mill them for 8 hours using zirconia balls as the grinding medium. After ball milling, dry the slurry at 80°C for 12 hours and pass it through a 120-mesh sieve. The median particle size of the resulting mixed powder is approximately 2.1 mm.

[0066] The mixed powder was placed into a graphite mold, spread and compacted, and then placed in a hot-pressing sintering furnace for vacuum hot-pressing sintering to prepare a plate-shaped green body with dimensions of 100 mm × 100 mm × 10 mm. The green body was pre-pressed at room temperature, then heated to 650℃ at 10℃ / min and held for 1 h to remove organic residues; then heated to 1600℃ at 5℃ / min and held for 60 min, with the pressure of the press head gradually increased to 8 MPa, and then heated to 1800℃ and held for 2 h before being cooled in the furnace.

[0067] The density of the sintered samples was tested using the water displacement method, and the sample density was ≥97%. The resulting composite shielding material mainly exists as a single-phase WB. Figure 10 The surface metallographic and SEM images of the material show excellent density and no porosity. The relative density difference between the center and the edge is less than 0.4%, and the room temperature magnetic permeability is 1.0018. Its room temperature magnetization curve is shown below. Figure 11 As shown, the sample surface is flat, with no obvious warping or cracking.

[0068] The room temperature compressive strength is 1344 MPa; gamma rays 60 The linear decay coefficient of Co is 0.72 cm⁻¹; the macroscopic cross section of the thermal neutron at 0.0253 eV is 178.5 cm⁻¹. -1 The half-value layer thickness is 0.0039 cm; the macroscopic cross-section of the 14 MeV fast neutron is 0.29 cm. -1 The thickness of the half-value layer is 2.38 cm.

[0069] The difference between this comparative example and Example 1 is that this comparative example uses a hot-pressing sintering process while adding Gd2O3 and ceramic and non-metallic sintering aids. It can be seen that the materials obtained by pressureless sintering in Example 1 and hot-pressing sintering in this comparative example are comparable in shielding performance, density, and mechanical properties. This indicates that the material obtained by the present invention using ceramic and non-metallic sintering aids, combined with spray granulation and cold isostatic pressing, and using a pressureless sintering process can achieve the same performance as the material obtained by the traditional hot-pressing sintering process. This shows that the present application, through the design of material composition and process, can achieve the densification co-firing of tungsten boride-Gd2O3 and the improvement of material mechanical properties using a pressureless sintering process, thus overcoming the limitations of hot-pressing sintering on mold shape and equipment cost, and is applicable to the continuous preparation of large-size plates, rings, and modular components.

[0070] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors, characterized in that, By mass percentage, it comprises the following components: 80.0–95.0% tungsten boride powder, 5.0–10.0% Gd₂O₃ powder, and 0.5–4.0% ceramic and non-metallic activating aids. The ceramic and non-metallic activating sintering aid includes an activating component and a stabilizing component. The activating component is B4C, and the stabilizing component is MgO or Y2O3.

2. The low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors according to claim 1, characterized in that, The content of B4C is 0.2% to 3.0%.

3. The low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors according to claim 1, characterized in that, The content of MgO or Y2O3 is 0.1% to 2.0%.

4. The low-magnetic, high-efficiency neutron and gamma composite shielding material for fusion reactors according to claim 1, characterized in that, The tungsten boride powder includes at least one of WB, WB2, and W2B5.

5. The low-magnetic, high-efficiency neutron and gamma composite shielding material for fusion reactors according to claim 1, characterized in that, The Gd2O3 powder has a particle size of 50–500 nm.

6. The method for preparing the low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Weigh out tungsten boride powder, Gd2O3 powder, B4C powder, and MgO or Y2O3 powder; S2. After mixing the raw materials, add the dispersion medium, dispersant and binder to form a uniform slurry; S3. After ball milling, the uniform slurry is spray-granulated to obtain a mixed powder with good flowability; S4. The granulated mixed powder is formed into a preform by low-pressure molding or pre-pressing, and then subjected to cold isostatic pressing. S5. The green body is sintered at high temperature.

7. The method for preparing a low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors according to claim 6, characterized in that, In step S2, anhydrous ethanol is used as the dispersion medium, isopropanol is used as the dispersant, and polyethylene glycol is used as the binder.

8. The method for preparing a low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors according to claim 6, characterized in that, In step S4, the pressure of low-pressure molding or pre-pressing is 5-50 MPa, and the pressure of cold isostatic pressing is 120-320 MPa.

9. The preparation method of the low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors according to claim 6, wherein the high-temperature sintering process in step S5 is as follows: Under vacuum or a protective atmosphere, the temperature is first raised to 1200–1500℃ and held for 0.5–2 h; then the temperature is raised to 1700–1900℃ and held for 1–4 h, and densification sintering is completed under pressureless conditions.

10. The method for preparing a low-magnetic, high-efficiency neutron-gamma composite shielding material for fusion reactors according to claim 9, characterized in that, In step S5, before high-temperature sintering, the temperature is raised to 300-700℃ and held for 0.5-3 hours to remove the glue and binder.

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